Device for heating preforms provided with supporting ring

ABSTRACT

A device for heating parisons made of a thermoplastic material and having a supporting ring for blow molding hollow bodies, having a conveyor means, a plurality of holding means which are arranged on the conveyor means and grip the head area of the parisons between the supporting ring and the mouth and radiant heaters arranged on the path of movement of the parisons carried by the holding means, a shield supported by the conveying means being assigned to each holding mandrel in the form of a cover plate which is located at the height of the supporting ring and has a borehole to receive the supporting ring. Furthermore, there is also a cooling device, which acts directly on the exposed head area. This permits optimum protection of the head area of the parisons, which is not to be shaped or deformed, to prevent unacceptable heating.

FIELD OF THE INVENTION

This invention relates to a heating apparatus for heating parisonsformed of thermoplastic material, such as used for forming beveragebottles in bottling operations.

BACKGROUND OF THE INVENTION

British Patent 2 095 611 B has already disclosed such a device withwhich the parisons are gripped on the outside in the head area by meansof holding fingers between the supporting ring and the open mouth andthe shielding is formed by a cylindrical protective jacket whichsurrounds most of the head area including the supporting ring. Althoughthe parison head area, which is not to be deformed, is protected fromdirect heating by the radiant heater due to this protective jacket, itis not protected from indirect heating by the protective jacket, whichis itself heated by the radiant heaters.

British Patent 2 095 611 B has already disclosed such a device withwhich the parisons are gripped on the outside in the head area by meansof holding fingers between the supporting ring and the open mouth, andthe shielding is formed by a cylindrical protective jacket whichsurrounds most of the head area including the supporting ring. Althoughthe parison head area, which is not to be deformed, is protected fromdirect heating by the radiant heater due to this protective jacket, itis not protected from indirect heating by the protective jacket, whichis itself heated by the radiant heaters.

SUMMARY OF THE INVENTION

The object of this invention is to improve upon the protection of thehead area of parisons, which is not to be deformed, to protect it fromunwanted heating in the case of a generic device.

In the case of a device according to this invention, the head area ofthe parisons is protected by the cover plates from direct heating due tothe radiant heaters. In addition, indirect heating via the closedprotective sleeves (not included) is prevented, and instead an activecooling of the head and thread areas is implemented. Because of thecontinuous shielding by the cover plates, which form a type of strip,this makes it possible to heat the area of the parisons, which is to beheated especially rapidly and in an energy saving manner in a closedheating channel, and to do so while the parisons are in the normalupright position.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described below onthe basis of drawings, which show:

FIG. 1 a schematic top view of a device for heating a parison;

FIG. 2 section A–B according to FIG. 1;

FIG. 3 a vertical section through a reflector belonging to the deviceaccording to FIGS. 1 and 2;

FIG. 4 the detail Z according to FIG. 2 in an enlarged diagram.

DETAILED DESCRIPTION OF THE INVENTION

The device 1 according to FIGS. 1 through 4 is set up for heatingparisons 2 made of PET, supplied at room temperature, to the processingtemperature between approximately 90° C. and 110° C., which is requiredfor stretch blow molding. It is integrated into a stretch blow moldingmachine, which is shown only schematically and in part, with a feederstar 13, a transfer star 14 and a blowing wheel 15, where hollow bodiesin the form of beverage bottles are produced from the preheated parisons2 by stretch blow molding.

The parisons 2, which are closed at the bottom, have a supporting ring 3in their upper area, and the head 5, which is located between the openmouth 4 and the supporting ring 3, has an external thread and is alreadyin its final form. The head 5 is not involved in the stretch blowmolding operation and therefore must not be heated in any case to atemperature close to the processing temperature in order to avoidunwanted deformation.

The device 1 has a continuous conveyor chain 12 having a plurality ofchain links 12 a of the same type which are joined together by pins inan articulated manner and have laterally protruding projections 12 b,which revolve in a horizontal plane over a driving wheel 16 and adeflecting wheel 17. Between the driving wheel 16 and the deflectingwheel 17, there are two parallel linear revolving regions, which movearound the wheels and in which the chain links 12 a are guided preciselyby means of stationary rails 19 and rollers 18, which are mounted on thechain links so they can rotate.

In at least one of the two linear revolving regions, a plurality ofsimilar stationary heating boxes 7 are situated on the path of movementof the parisons 2, which are carried by the conveyor chain 12, each boxbeing equipped with a plurality of horizontally aligned tubular infraredlamps 36.

A sleeve 20 having a vertical rotational axle is mounted in eachprojection 12 b of the conveyor chain 12 and is connected in arotationally fixed manner to a toothed wheel 21; it engages with astationary toothed rack or a continuously revolving roller chain 21 andsets the sleeve 20 in continuous rotation when the conveyor chain 12 isrotating continuously. A holding mandrel 6 is accommodated in eachsleeve 20 in a rotationally fixed manner but with an adjustable height.The holding mandrel projects out of the bottom side of the sleeve 20 andis rigidly connected to a control rod 22 which projects at the upper endof the sleeve 20. A compression spring 23 which presses the holdingmandrel 6 into its upper end position shown in FIGS. 1 and 2 is insertedbetween the broadened end of the control rod 22 and the sleeve 20, thisposition being defined by stops (not shown). With the help of controlrod 22 and stationary curve ramps (not shown), the holding mandrel 6 maybe moved into its lower end position (indicated with a dash-dot line inFIG. 2) against the force of the compression spring 23. This liftingmovement serves to introduce the holding mandrel, which is equipped witha spring ring, into the open mouth 4 of the parison 2 in the area of thefeeder star 13 and for extraction out of the mouth 4 in the area of thetransfer star 14.

On the lower side of each projection 12 b of the conveyor chain 12, ahorizontal cover plate 8 having a square periphery is attached at adistance by means of four thin perpendicular rods 11. The cover plate 8consists of an essentially flat piece of sheet metal several millimetersthick or a profiled molded part, and it has a central borehole 9, whichis concentric with the sleeve 20 and the holding mandrel 6. The diameterof the borehole 9 is slightly greater than the outside diameter of thesupporting ring 3. The height and thickness of the cover plates 8 areselected so that the supporting ring 3 of a parison 1 is situatedcentrally in the borehole 9 at a slight distance of 2 to 3 mm, forexample, from the bottom side of the cover plate, and most of the head 5projects above the top side of the cover plate 8 and is thus freelyaccessible from practically all sides between the four rods when theholding mandrel 6 with the parison 2 placed on it assumes its upper endposition (see FIG. 4). In the lower end position, however, there is aparison 2, which is to be gripped or released by the holding mandrel 6,with its mouth 4 situated at a slight distance beneath the cover plate8.

The heating boxes 7, which are arranged in a line on the outside of thelinear peripheral area of the conveyor chain 12, form a linear heatingchannel K together with plate-shaped ceramic reflectors 35, which arearranged in a line on the inside of the linear revolving area, and aceramic base plate 26; the parisons 2, which are conveyed in the normalupright position, project from above with their body area 24 which is tobe shaped, into the linear heating channel. The heating channel K isclosed at the upper end by the cover plates 8, which come in contactwith one another or are opposite one another at a slight distance andform a revolving belt of cover plates in combination with a linearcooling shield 27 through which water flows on the side of the heatingboxes 7 and a baffle plate 28 on the side of reflectors 25. The linearedges of the cooling shield 27 and the baffle plate 28, which pointtoward one another and run parallel to one another are arranged at asmall distance from the cover plates 8 or they come in contact with thelatter. Due to the design of a heating channel K, which is closed on allsides, this permits an extremely effective and energy-saving heating forthe body area 26, which is to be shaped beneath, the supporting ring 3of the parisons 2. To prevent overheating of the surface of the parisons2, narrow slotted nozzles 29 are provided between the heating boxes 7with fans 30 connected to them, to blow room air in a high concentrationonto the surfaces of the parisons 2 as they revolve past them.Furthermore, a cooling fan 31 is connected to the outside of eachheating box 7 to cool the infrared lamps 36. The air which is introducedby the fans 30 and 31 into the heating channel K at an excess pressureis removed through perpendicular slot-shaped orifices 37 providedbetween the individual reflectors 25. These orifices 37 are eitherpositioned in a single inclination relative to the direction of emissionof the infrared lamps 36, as shown in FIG. 1, or they are positioned sothat there are two inclinations, as shown in FIG. 3. This prevents thethermal radiation emitted by the infrared lamps 36 from being able toescape directly through the orifices 37. The orifices 37 open into acollecting channel 38 through which the heated air from the heatingchannel K coming from the fans 30, 31 is discharged from the device 1 ina controlled manner. Because of the arrangement described here, the head5 of each parison 2 is situated completely outside of the heatingchannel K and is protected optimally from direct heating by the infraredlamps 36 due to the cover plates 8, which are carried by the conveyorchain 12. To prevent any indirect heating by heated parts of a device,etc., a separate cooling system 10 is provided for the heads 5. It hasone or more nozzles 39 which are situated on the inside of the linearperipheral area of the conveyor chain 12 and supply ambient air throughfans 40. If necessary, a heat exchanger 41 which has a coolant flowingthrough it may also be provided in the nozzles 39. Intense cooling ofthe head 5 of the parison 2, which is freely accessible for the mostpart, is achieved by the cooling device 10. In addition, this also coolsthe adjacent parts of the device 1, such as the holding mandrels 6, etc.The air is guided by appropriate baffle plates in countercurrent withthe air flow in the heating channel K and to some extent also throughthe cooling shield 27.

The cover plates according to this invention can be used in the same waywith parisons in which the supporting ring is not formed on a projectingneck collar, but instead on a recessed ring groove, especially shapedtransition between the head and the body, etc. It is important only thatthe cover plate be arranged at the dividing point between the area ofthe parison to be shaped further and that which is not to be shapedfurther.

If the parisons are heated in the normal upright position, as shown inthis embodiment, the cover plates according to this invention alsoprevent heating of the head area due to hot air ascending out of theheating channel. The parisons can therefore be heated with no problem ina normal position without first rotating them by 180°.

1. A device for heating parisons (2) made of a thermoplastic materialfor blow molding hollow bodies and having a body area (24), a supportingring (3), a mouth (4), and a head area (5), comprising a conveyor means(12), a plurality of holding means (6) which are situated on theconveying means and grip the head area (5) of the parisons between thesupporting ring and the mouth (4), radiant heaters (36) arranged on thepath of movement of the parisons which are carried by the holding means,a shield carried by the conveying means provided for each holding meansto protect the head area of each parison, which is situated between thesupporting ring and the mouth, from heating each shield being formed bya cover plate (8) arranged at the level of the supporting ring (3) andhaving a borehole (9) that surrounds the supporting ring (3) at a smalldistance, thereby leaving most of the head area (5) of the parisons (2)free, and a cooling device (10) which acts on the exposed head area (5)of the parison (2), wherein each cover plate (8) is designed in themanner of a plate and is connected by at least one rod (11) to theconveyor means (12) and the cooling device (10) has at least one airblowing nozzle (39) directed at the head (5) of the parisons (2).
 2. Thedevice according to claim 1, wherein the conveyor means are formed by acontinuous conveyor chain (12) having at least one linear revolving areain which the radiant heaters (36) are arranged, the cover plates (8)have one of a rectangular and square periphery, and adjacent coverplates (8) one of contact one another in the linear revolving area ofthe conveyor chain (12) and they are opposite one another with a slightdistance between them.
 3. The device according to claim 2, wherein theparisons (2) are transported in a freely suspended manner in an uprightnormal position with the mouth facing upward on holding mandrels (6),and with their body area (24) they are immersed in a heating channel (K)comprising a radiant heater (36) and diametrically opposed reflectors(25), the heating channel being covered at the top by the cover plates(8).
 4. The device according to claim 3, wherein a plurality of coolingfans (30,31) are connected to the heating channel (K) on the side of theradiant heaters (36), and orifices (37) for removing the cooling airfrom the heating channel (K) are provided on the side of thereflectors(25).
 5. The device according to claim 1, and a heat exchanger(41) through which a coolant flows is arranged in the air blowing nozzle(39).
 6. The device according to claim 1, wherein the holding means areformed by holding mandrels (6) which are arranged on the conveyor means(12) in such a way that they are adjustable in height and can beinserted beneath the mouth (4) of the parisons (2).